1. Field of the Invention
The present invention relates to a semiconductor device, a display device, a liquid crystal display device, and a light-emitting device and a method for manufacturing these devices. In particular, the present invention relates to a semiconductor device, a display device, a liquid crystal display device, and a light-emitting device each of which includes a circuit having a transistor including an oxide semiconductor film, and a method for manufacturing these devices.
2. Description of the Related Art
Thin film transistors (TFTs) in which silicon layers formed using amorphous silicon or the like are used for channel layers have been widely used as switching elements in display devices typified by liquid crystal display devices. Although thin film transistors formed using amorphous silicon have low field-effect mobility, they have an advantage that larger glass substrates can be used.
Moreover, attention has been recently drawn to a technique by which a transistor is manufactured using a metal oxide with semiconductor properties and such a transistor is applied to an electronic device or an optical device. For example, it is known that some metal oxides such as tungsten oxide, tin oxide, indium oxide, and zinc oxide have semiconductor properties. Patent Document 1 discloses a transistor in which a transparent semiconductor layer formed using such a metal oxide is used as a channel formation region.